Soy protein concentrates and soy protein isolates are important derivatives of soybeans which are used primarily as food and feed ingredients. Conditions typically used to prepare soy protein isolates have been described by Cho, et al, (1981) U.S. Pat. No. 4,278,597; Goodnight, et al, (1978) U.S. Pat. No. 4,072,670!. Soy protein concentrates are produced by three basic processes: acid leaching (at about pH 4.5), extraction with alcohol (about 55-80%), and denaturing the protein with moist heat prior to extraction with water. Conditions typically used to prepare soy protein concentrates have been described by Pass (1975) U.S. Pat. No. 3,897,574; Campbell et al., (1985) in New Protein Foods, ed. by Altschul and Wilcke, Academic Press, Vol. 5, Chapter 10, Seed Storage Proteins, pp 302-338!. In the production of soy protein isolates and soy protein concentrates, the soluble sugars present in the dehulled, defatted soybean meal contain stachyose and raffinose Dey, (1985) Biochemistry of Storage Carbohydrates in Green Plants, Academic Press, London, pp 53-129!. Stachyose and raffinose are not digested directly by humans and animals but, rather, by microflora in the lower gut. These microflora are able to ferment these sugars thus resulting in an acidification of the gut and production of carbon dioxide, methane and hydrogen Murphy (1972) Journal of Agricultural Food Chemicals 20 pp 813-817, Cristofaro 91974) Sugars in Nutrition Chapter 20, pp 313-335, Reddy (1980) Journal of Food Science 45 pp 1161-1164!. The resulting flatulence can severely limit the use of soybeans in human and animal diets. These sugars are removed in the production of soy protein isolates and soy protein concentrates and treated as a waste product of the manufacturing process. This waste represents a minimum of 25% loss of the original dehulled, defatted soy flake raw material. Additionally, the treatment of these wasted sugars is a considerable manufacturing cost factor in the production of soy isolates and concentrates, and the waste processing is an important factor that can limit the location of a factory to produce such products. The incorporation of these sugars into soy isolates or concentrates would significantly reduce production costs, reduce the amount of equipment necessary, and by eliminating waste treatment options the opportunities in site selections for such factories would be improved.
Isoflavones are naturally occurring components of soybeans which are present in soy foods and soy protein isolates and concentrates. It has been suggested that such isoflavones in soy products may have a potential role in the prevention of cancer, Messina and Barnes (1991) Journal of the American Cancer Institute, Vol. 83, No. 8 pages 542-545. It has been suggested that the isoflavone genistein may have some role as a chemopreventive agent against breast and prostate cancer in humans, Peterson and Barnes, 1991, Biochemical and Biophysical Research Communications 179, pp 661-667 and Peterson and Barnes (1993), Prostate 22, pp 335-345. The concentration of isoflavones present in defatted soybean meal is significantly reduced in the production of soy protein isolates and concentrates, and such reduction is significantly dependent on the manufacturing process Wang and Murphy (1994) Journal of Agricultural and Food Chemistry,42, pages 1665-1673!. Increasing the concentration of isoflavones present in soy protein isolates or concentrates is desirable, but existing commercial processes capture only 3 to 35% of the isoflavones available in the raw material.
Soy protein isolates and concentrates are used in the food industry to replace or extend meat, milk, egg, and other protein sources in traditional food products. The soy proteins are modified to have similar functional performance as the protein being replaced or extended. Some of the major applications where soy protein isolates and concentrates are used include emulsified meats, whole muscle injection meats, ground meats, infant formulas, nutritional beverages, milk replacers, imitation processed cheese spreads, and dairy products. One of the key factors limiting the use of soy protein isolates especially in nutritional beverages, milk replacers, and dairy products is the soy taste present in the isolates. If the traditional soy taste could be masked or reduced, significant increases in soy isolates usage levels in the identified applications would occur. Soy concentrates are not widely used in the applications of nutritional beverages, milk replacers, and dairy products because of the strong soy taste and the presence of soy fiber as an insoluble component with undesirable mouthfeel. Reducing the level or masking the soy taste would allow for limited improvement in usage in these applications as the fiber would remain a significant negative factor.
Commercial manufacturing procedures for soy isolates results in products with lower levels of the sulfur containing amino acids cysteine and methionine when compared to soy concentrates. Cysteine and methionine are essential amino acids which are important nutritional factors in all soy products as well as other products produced from meat, milk or egg proteins.
The development of a process which would produce a soy protein product with an improved carbohydrate profile, increased isoflavone content, improved flavor profile, acceptable mouthfeel, improved nitrogen solubility index, and increased sulfur containing amino acid composition would dramatically increase the utilization of soy protein products as food ingredients. In addition, such a process would significantly improve the cost of production by reduction of operating costs, improvement in raw material conversion, and allowing greater flexibility for manufacturing site selection as well as eliminating waste treatment costs.